The skin is the largest organ of a mammalian body, serving many important functions, such as regulating body temperature, maintaining water and electrolyte balance, and sensing painful and pleasant stimuli. The skin is adapted to keep dangerous substances from entering the body and provides a shield from the harmful effects of the sun. Any deterioration in skin health may have important consequences on a person's physical and mental health. Many teenagers suffer from acne, which is an inflammatory disease of the skin, caused by changes in the pilosebaceous units and results in scarring or hyperpigmentation of the skin. Several types of skin disorder manifest themselves as rashes and lead to itching. The itching and rashes may develop as the result of infection or irritation or from an immune system reaction. Additionally, the skin is prone to microbial infection and parasitic infestation.
External topical administration is an important route for the administration of drugs in both systemic and topical disease treatment. Many groups of drugs, including, for example, antibiotic, anti-fungal, anti-inflammatory, anesthetic, analgesic, anti-allergic, corticosteroid, retinoid and anti-proliferative medications are preferably administered in hydrophobic media, namely ointment. However, ointments often form an impermeable barrier, thus in the treatment of a topical wound, metabolic products and excreta from these wounds to which they are applied are not easily removed or drained away. Furthermore, it is difficult for the active drug dissolved in the carrier to pass through the white petrolatum barrier layer into the wound tissue, so the efficacy of the drug is reduced. In addition, ointments and creams often do not create an environment for promoting respiration of the wound tissue and it is not favorable to the normal respiration of the skin. An additional disadvantage of petroleum jelly-based products relates to the greasy feeling left following their topical application onto the skin, mucosal membranes and wounds. A further problem of non aqueous compositions is achieving formulations in which the active agent is stable.
Some active agents are known to be generally unstable or susceptible to isomerisation or to breakdown, resulting in loss of activity and the use of stabilizers, anti oxidants antimicrobials and buffers and the like in aqueous compositions to protect active or cosmetic agents is known. The problems of protecting active pharmaceutical and cosmetic agents in waterless environments, such as polar compositions are multifold and can vary according to the type of waterless environment and the nature of the agent being used. It has been surprisingly found that factors like small levels of acid residues in the raw materials can be significant in influencing agent stability. Similarly, the presence of low levels of metal ions can act to catalyze reactions or breakdown. Likewise, the presence of agents in a waterless environment that results in ionization or leads to oxidation can act to cause reactions or breakdown. There is therefore a need for simple and elegant solutions to stabilize active ingredients in a waterless or substantially environment.
It would be particularly advantageous and there is an unmet need to have a waterless vehicle additive that is suitable for use not merely one type of active pharmaceutical ingredient (API) but is adaptable for use with one or more API's from a wide range of different types of API's with relatively minimal or minor adjustment.
Foams and, in particular, foam emulsions are complicated systems which do not form under all circumstances. Changes in foam emulsion composition, such as by the addition of active ingredients may destabilize the foam. There is, therefore, a need for a foam composition, which provides desirable properties to the skin and can remain stable whilst accommodating a variety of active ingredients.
Formulations based on oil or ointment or emollients have a number of useful attributes making them suitable candidates for topical pharmaceutical and cosmetic compositions including foamable compositions. They are inherently stable and inert which are clearly desirable characteristics. They are able to moisturize and soften the skin and in appropriate amounts can act as a protective or barrier layer and can form a barrier to water. By appropriate formulation they can act to improve drug delivery to the skin and yet remain resistant to being washed off. On the other hand they are by their nature greasy materials and can be difficult to formulate particularly into a topical foamable composition that can deliver substantially uniform and stable composition or foam that ameliorates or overcomes the look and feel of a greasy material, especially where that composition is waterless or substantially so. It is further a problem to incorporate into such a vehicle pharmaceutically effective amounts of one or more active pharmaceutical ingredients such that they are uniformly present throughout the formulation and are effectively delivered without the use of an alcohol in the formulation.
On one level it is far from simple or obvious to produce waterless foamable compositions that when released produce foams of quality suitable for pharmaceutical or cosmetic application. On a further level having realized a carrier that will produce a waterless foam of quality there is an additional difficulty to be overcome, namely how to adapt the formula and achieve a formulation, which can accept a range of various active pharmaceutical and cosmetic agents such that the composition and active agent are stable and the foam produced remains of quality. Specifically, one of the challenges in preparing such waterless or substantially waterless foamable compositions is ensuring that the active pharmaceutical or therapeutic agent does not react, isomerizes or otherwise break down to any significant extent during is storage and use. Particularly, there remains an unmet need for improved, easy to use, stable and non-irritating foam formulations, with unique therapeutic or beneficial properties containing a stable or stabilized active pharmaceutical or cosmetic agent.
There remains an unmet need for improved, easy to use, stable and non-irritating topical foam formulations containing a stable or stabilized active pharmaceutical or cosmetic agent having a therapeutic or beneficial effect, intended for treatment of dermal and mucosal tissues.
Systemic administration of active agents often leads to allergic responses, side effects and bacterial resistance to the active agents. There thus remains an unmet need for improved, easy to use, stable and non-irritating anti-infective foam formulations comprising active agents, intended for treatment, inter alia, of dermal and mucosal tissues. Particularly, there remains an unmet need for improved, easy to use, stable and non-irritating anti-infective foam formulations, with unique therapeutic properties.
Foams are complex dispersion systems which do not form under all circumstances. Slight shifts in foam composition, such as by the addition of active ingredients, may destabilize the foam. Foams are very complex and sensitive systems and are not formed at will. Mere addition of basic ingredients like oil, surfactant and propellant is far from sufficient to produce foams of quality that are homogenous, stable, breakable upon mechanical force and can be used to provide a shelf stable pharmaceutical or cosmetic composition. Small deviations may lead to foam collapse. Much consideration needs to be given to facilitate the introduction of an active agent, such as examining compatibility and non reactivity with the various excipients and container and determining shelf life chemical stability.
Neubourg (US 2006/0099151), for example, notes that the stability of foam is strongly dependent on the specific composition of the foam forming components, so that even small deviations in the composition may lead to a collapse of the foam. Gordon et al. (U.S. Pat. No. 3,456,052). also teaches that one cannot generate a good quality foam by simply adding a propellant to a mixture of components:
The term “foam” is a general term that encompasses a range of substances. Accordingly, the context in which “foam” is discussed must be examined carefully. The type and quality of the foam is of critical importance. There are many different types of foams and within each foam type there are many levels of qualities. For example, the froth on the head of beer, lather of shampoo, and lather of shaving cream have been loosely described as foam but all are different from one another. At one end of the cosmetic or pharmaceutical foam spectrum the foam can be long lasting and essentially not readily breakable like shaving foams. At the other end of the spectrum the foam can be quick breaking and collapses upon release.
Thermolabile foams are an example of type of quick breaking foam. They can contain significant amounts of thermolabile substances that aid their collapse upon being exposed to an increased temperature for example when applied to a body surface at 37 C. Upon being exposed to the higher temperature they collapse rapidly. Examples are foam formulations that comprise significant amounts of volatile solvents.
Breakable foam is a specialized type of foam. It is a low density foam that is stable on release at least in the short time span of several minutes, which facilitates application to a target area; but can break readily upon the application of shear force such as gentle rubbing to spread easily over a target surface. It is not thermolabile (and does not melt at skin temperature) and nor does it display late or long delayed expansion over minutes.
Some foams expand slowly whilst others do so quickly. Some foams foam immediately and some demonstrate delayed foaming. Some require mechanical lathering and some expulsion by propellant. Whilst they all fall under the so called term “foam” and may appear to have some common ingredients the results and properties of these products are different.
A suitable foamable formulation for a particular application may present challenges at several levels. For example, a foam formulation may require a stable pre foam formulation; a stable pre foam propellant formulation and ultimately delivery an effective measured amount of active agent to a target. Each of these objectives poses its own unique challenges.
The pharmaceutical and cosmetic foams discussed herein are generated in general terms by manufacturing a suitable foamable carrier composition and loading the carrier in a pressurized valved canister with an appropriate propellant. Upon expelling the canister contents a foam can be released. The type, nature and quality of the foam depends inter alia on the carrier composition, the active agent, the propellant and the method of manufacture and storage. Making a stable (physically and chemically) formulation that can be stored in a canister with a propellant that remains stable and can produce a breakable foam of quality on release is far from trivial.
An additional difficulty frequently encountered with propellant foams is their inability to dispense a uniform application of the medically active ingredient throughout the use of the entire aerosol container. This is particularly due to the fact that the active material is not stably dispersed in the foamable composition so that it will have a tendency to settle to the bottom. Further, the dispersed material will sometimes clog the spray dispensing valve to further interfere with the uniform dispensing of the medicament.